1. Field of Invention
The invention relates to an inverter and a driving device of a backlight module. More particularly, the invention relates to an inverter having an electric-isolating function, and a driving device of a backlight module.
2. Related Art
In general, a liquid crystal display (LCD) device includes a backlight module and a LCD panel. The backlight module mainly drives a light-emitting unit by a driving device, and thus provides a backlight source for the LCD device.
Referring to FIG. 1, a typical driving device 1 of a backlight module includes a power factor correcting circuit 11, a DC-to-DC power transforming circuit 12 and a DC-to-AC power transforming circuit 13 which is the so-called inverter. This architecture is usually referred to as the three-stage architecture.
The power factor correcting circuit 11 transforms a mains power (AC power) into a DC power with 400 volts. The power factor correcting circuit 11 mainly functions to make the voltage and the current in the circuit have the same phase such that the load approximates a resistive load and a better use efficiency can be obtained.
The DC-to-DC power transforming circuit 12 is electrically connected to the power factor correcting circuit 11 for dropping down the voltage of the DC power with 400V and thus outputting a DC power having a voltage lower than 400V. In addition, the reference voltage terminal of the rectified mains power is isolated from the ground of the load (light-emitting unit) in the DC-to-DC power transforming circuit 12 to prevent a user from being dangerously shocked due to the circuit formed by the user and the mains power when the user touches the ground of the load.
The DC-to-AC power transforming circuit 13 is electrically connected to the DC-to-DC power transforming circuit 12, and again transforms the DC power outputted from the DC-to-DC power transforming circuit 12 into an AC power for driving and thus lighting the light-emitting unit.
Recently, a driving device with the two-stage architecture has been disclosed, in which a DC-to-DC transforming circuit is omitted, and the DC power outputted from the power factor correcting circuit is directly transmitted to the inverter. Consequently, the cost of the DC-to-DC transforming circuit can be saved. However, the isolating function provided by the DC-to-DC transforming circuit has to be transferred to the inverter. The typical manufacturer uses an isolated transformer as a boost transformer in the inverter, so the size of the inverter is enlarged. In addition, the number of light-emitting units used in the backlight module is increased as the size of the LCD device is increased. Therefore, many sets of inverters are inevitably needed to drive the light-emitting units. Of course, the size and the manufacturing cost of the inverter are greatly increased therewith.
Therefore, it is an important subject of the invention to provide an inverter, which has a small size, an effectively decreased cost and an electric-isolating function, and a driving device of a backlight module.